65 million years ago, at the same time as
the dinosaurs. Remains of pterodactyls
have been found all over the world.
As far as scientists know, pterodactyls
were the largest flying animals that ever
lived. Some pterodactyls measured more
than 36 feet (11 meters) across with the
wings spread out. But the smallest pterodactyls
were as small as a sparrow.
A pterodactyl’s back legs were long and
thin, like those of birds. Pterodactyls
also had long beaks. But unlike birds,
pterodactyls did not have feathers. Their
wings were made of skin, like those of
bats. Pterodactyls probably did not fly
by flapping their wings constantly.
Instead they probably glided on air currents.
Pterodactyls were meat eaters. Many had
hooked claws and sharp teeth that they
used to grab and hold onto prey. Pterodactyls
that lived near water fed mostly
on fish. Pterodactyls that lived far from
water ate small animals.
#More to explore
Dinosaur • Prehistoric Life • Reptile
Public Health
The term public health describes efforts
to keep a whole community healthy.
Local and national governments run
many public-health programs. These
programs improve living conditions and
give people longer lives.
Public health includes many different
health services. Some programs work to
prevent and to fight disease. Vaccination
is an important part of these efforts. A
vaccine is a substance given to people to
protect them from illness. Other programs
focus on fighting pollution or
keeping food and water safe. Public
health also involves teaching people
about exercise and healthy eating.
Public-health programs started to appear
in the 1700s and 1800s. Before that,
health was mostly a personal or local
issue. But as the populations of cities
and countries grew, the number of
health problems grew, too. Governments
began to see the need for keeping the
A fossil skeleton shows that pterodactyls
must have looked like giant birds. But scientists
do not believe that birds came from
pterodactyl ancestors.
Obesity, an
extreme form
of being overweight,
has
recently
become a
major publichealth
issue in
the United
States.
BRITANNICA STUDENT ENCYCLOPEDIA Public Health 163
public healthy. Today most countries
have their own public-health programs.
In the United States, the Department of
Health and Human Services oversees
many public-health agencies.
The World Health Organization
(WHO) promotes the health of people
around the world. It works to stop the
spread of polio, AIDS, and other diseases.
Its vaccination programs helped
rid the world of smallpox. The WHO
also warns travelers about diseases in
certain countries.
#More to explore
Government • Vaccine
Pueblo
The Pueblo are a group of Native
American tribes that live in northeastern
Arizona and northwestern NewMexico.
Early Spanish explorers gave them the
name Pueblo, which is Spanish for
“village” or “town.” The explorers were
impressed by the villages that the Indians
had built. Today the term pueblo is used
for both the people and their villages.
The Pueblo built large houses that had
several stories, like apartment buildings.
They used blocks of adobe, or sunbaked
clay. The Pueblo got most of their
food from farming. Their main crop was
corn. Early Pueblo also hunted and
gathered wild plants to eat.
The Pueblo are descendants of the
ancient Anasazi people. Some of their
villages were already hundreds of years
old when Spanish soldiers arrived in
1540. The Spanish gave the Pueblo
metal tools and cloth. They also brought
horses and new crops such as wheat and
chili peppers.
Later Spanish rulers were cruel to the
Pueblo. In 1680 a Pueblo leader called
Pope led a rebellion against the Spanish.
The Pueblo drove the Spanish from
their lands for 12 years. When the Spanish
returned they had more respect for
the Indians. Their rule was not as harsh.
People wait in line to get flu shots. Such
shots can prevent diseases from spreading
to many people in a community.
A photograph from the early 1900s shows
adobe houses built by the Zuni, a group of
Pueblo Indians.
164 Pueblo BRITANNICA STUDENT ENCYCLOPEDIA
At the end of the 20th century there
were about 60,000 Pueblo Indians. They
lived in 19 pueblos. Unlike many other
Indians, modern Pueblo have mostly
been able to keep their traditional way
of life.
#More to explore
Adobe • Anasazi • Native Americans
Puerto Rico
Puerto Rico is an island in the Caribbean
Sea. It is a commonwealth of the
United States. This means that Puerto
Rico governs itself but keeps some ties
with the United States. The capital of
Puerto Rico is San Juan.
Puerto Rico is part of the island group
called theWest Indies. The island is
roughly rectangular in shape. It is mostly
mountainous, but the land along the
coast is flatter. The weather is warm
year-round.
Most Puerto Ricans have Spanish ancestors.
People of African descent make up
a smaller group. Some people have
mixed European and African roots.
Most Puerto Ricans speak Spanish, and
many speak English as well. Most of the
people are Christian.
Puerto Rico’s main sources of income
are manufacturing, services, and trade
with the United States. Factories make
chemicals, medicines, electronics,
